The objective of this research is to study the action of barbiturates, on electrical brain activity (contingent negative variation or CNV) and related psychophysiological functions in humans. Two studies currently are being conducted: an investigation of the action of fast and slow acting barbiturates 1) in normals, and 2) in barbiturate addicts during withdrawal from barbiturates. Preliminary findings based on 15 normals and 4 addicts are as follows: 1. In normals, phenobarbital tends to have a stronger and more lasting effect on CNV amplitude than does pentobarbital. 2. Two hours after ingestion, phenobarbital tends to decrease CNV amplitude in normals and increase CNV amplitude in barbiturate addicts. The decreased CNV amplitude in normals produced by phenobarbital appears to be accompanied by deterioration in psychomotor performance (lower reaction time). 3. Although normals and barbiturate addicts are comparable on a number of electrophysiological and behavioral measures made prior to ingestion of barbiturates, barbiturate addict subjects tend to show a greater pre-ingestion variability in a number of scores than do normal subjects. 4. Soon after ingestion of barbiturates, when CNV amplitude decreases in both normals and barbiturate addicts, subjective reports of vigor decrease in normals (as does CNV amplitude) but markedly increase in barbiturate addicts (in contrast to CNV amplitude).